is that the same multiplication that any lens would get from a cropped frame? ... i.e. if i got the sony 11-18mm its lower end would be comparable?

The sigma website says the lens fits sony as well :s

Sigma make different versions of their lenses for different brand of cameras. So they make a 12-24 for a Nikon, for a Canon, for a Sony etc. but they are different lenses and the Sigma lenses built for Nikons won't fit on Canon or Sony cameras.

is that the same multiplication that any lens would get from a cropped frame? ... i.e. if i got the sony 11-18mm its lower end would be comparable?

Yes, any DSLR that uses an APS-C sized sensor will have a zoom factor of 1.5 compared to the traditional full frame DSLR and film cameras. That means that your 12 - 18 mm lens will will be equivalent to 18 - 27mm on the APS-C sensors.

You should multiply all focal lengths you see by 1.5 if you want to work out what it actually is on an APS-C sensor.

Quote:

The sigma website says the lens fits sony as well :s

Sigma makes lenses for most cameras. However, each lens mount (i.e. the connector that links the lens to the camera) is different. So a Sigma lens that has the Nikon AF mount will not work on Canon and Sony cameras and vice versa.

Keep in mind that the Sigma 12-24mm will fit on future full frame bodies, but the Sony 11-18mm won't. If you think you might buy a full frame camera some day, the Sigma may be a better choise. Just make sure you get the Sony-mount version though .